Continuity test apparatus



Patented Sept. 9, 1952 2,610,229 NTINUITY TEST APPARATUS :1 Jesse A. Cranford, Buffalo, N. Y., assignor .to Western Electric Company, Incorporated, New

York, N. Y., a corporation of-New York Application September 16,1950, Serial No. 185,283

This invention relates to testing apparatus and more particularly to a test circuit for determining the condition of electrical conductors.

In connection with the manufacture of electrical conductors, it is customary to test the conductors before shipment to determine if they contain open circuits or if groups of conductors contain short circuits. Similar tests are often necessary after the conductors have been placed in service, to discover subsequent defects. Since this testing is usually done one wire at a time, the operation becomes laborious and time consuming, and there has been a need for apparatus which would expedite such tests. It istherefore an object of this invention to provide such apparatus. 'A A A Applicant accomplishes his object according to the invention by applying voltages in quadrature across the diagonals ofAa bridge to whose terminals are connected four wires to be tested. Application of the voltages causes lamps located in the bridge arms and diagonals to give a simultaneous indication of the good or shorted condition of all possible pairs. Five conductors may be tested simultaneously by connecting the fifth conductor to the midpoints of the diagonals, while, if the far ends of the conductors are bonded together, the apparatus indicates the existence of open circuits. A A A Other objects and advantages will be apparent from the following detailed description taken in conjunction with the attached drawings in which: q A

Fig. l is a schematic wiring diagram of the circuit used for simultaneously testing four conductors; A

Fig. 2 shows the phase relationship between the two voltages impressed across the test circuit; l l

Fig. 3 is a schematic wiring diagram ofthe circuit used for testing five conductors simultaneously. l A

With referenceto Fig. l of the drawing, four electrical conductors ll, l2, l3, and H to be testedare connected to terminals 15, I6, I1, and [8 of a Wheatstone bridge generally designated as 20. These conductors may be individual wires or may be part of a cable 6 as shown, and may be connected directly to the bridge terminal or through an intermediate switch I, which may take the form of a telephone Jack. The bridge has four arms 2|, 2!, 23, and 24, and two diagonal bridge connections and 26. Indicating lamps 2T, 28, 29, 30, 3|, and 32 are connected in series in the bridge arms and diagonal connections, as shown on the drawing.

A potential El, supplied from a secondary winding 33 of a transformer 34 is impressed across the terminals l5 and I1 ofthe bridge. A potential E2,Ataken from secondary winding 35 of the transformer, is correspondingly impressed across terminals 16 and 18 of the bridge. It is desirable 4Clai ns. (01.175-183) that these voltages be approximately '90 electrical degrees apart and to this end an inductance 36 is connected into the circuit for voltage E2 and a capacitance 31 is inserted in the circuit for tween any pair of conductors, say, between wires II and [2, it is obvious that the voltage across the arm 2| is effectively shortcircuited, thus bringing terminals 15 and I6 to the same potential and causing the indicating lamp 2! in that arm to be extinguished. A short circuit between conductors l2 and l3will likewise place terminals I6 and I! at the same potential and cause the lamp 28 in that arm to go out. Should a short circuit exist simultaneously between all of the conductors, all of the indicating lamps will be extinguished, thus revealing the multiple short condition.

It will therefore be seen with reference to Fig. 1 that any short circuit or combination of short circuits between the four conductors undergoing test will cause the corresponding indicating lamps to go out, thus designating the defective conductors. The proposed circuit therefore enables the four conductors to be tested simultaneously for this condition without the need for multiple switching. A

Applicant has discovered that in order to make this simultaneous test, the pair of impressed voltages should be displaced approximately from each other. For the test to be successful, it is necessary that the indicating lamps remain lit at all times when no short circuit exists, which means that there must always be 'a resultant voltage across the bridge arms and diagonals. If, for example, two sources of direct current of equal value were used, as El and E2, it will be obvious that in two of the main four arms 2|, 22, 23, and '24 of the bridge, the impressed voltages would cancel each other, thus causing the lights in these armsto be out even though a short circuit condition did not existe The use of two alternating potentials which were in phase would have the same effect as the use of direct current in that the voltages across two of the bridge arms would cancel each other. The use of two alternating potentials exactly out of phase: would also have the same efiect, as it would amount to no more than reversing the terminal connections of one of the D. C. sources. l

By placing the two impressed voltages in quadvoltage across each of the bridge arms and volt age across the diagonals to cause the correspond-.

ing lamps to light in the absence of a short cir cuit condition. These two voltages will of course cancel each other momentarily in the various bridge arms twice in each cycle, but as this con-' obtained with voltage displacements somewhat above or below this figure. However, for-best results the voltage displacement should approximate 90.

With further reference to Fig. 1, thefour-leads under test are shown connected to a switch as which may be closed to connect all the leads together at 4!. The use of'this shorting switch enables all of the four conductors l I, I2, l3, and Hi to be tested simultaneously for continuity, as the simulated short circuit condition imposed on the wires causes all of the indicating lamps to go out unless there is an open circuit in one or more of the leads; Should conductor ii, for example, contain an open circuit, there would be no effective short circuit between terminal Iii of the bridge and terminals-l5, it, and ii; and-as a result, the three lamps :30, 32, and 29 associated with the terminals l8 and lead id would not be extinguished. It is thus possible to tell at a, glance which, if any, of the four'conductor under test contains an open circuit.

Fig. 3 shows the circuit applied to the 31111111".

taneous test of five conductors insteadof fourj This is done by joining the diagonals of-the bridge at the point 59 to form diagonal arms 51, 52; 53,

and 54, these arms having'located therein in:

dicating lamps 55, 56, 51,- and 53. The short circuit test for the five conductors ii, i2, i3; i i,

7 and 60 works on the sameprinciple and in the same manner as the test involving four conductors. However, onedifference between the 1 two tests will be that a short condition'between wires ii and i3 and between wires i2 and i l will be indicated by the extinguishing of-two lamps instead of .oneynamely, by lamps'55 and;5i-and lamps 56 and, 58 respectively. Fora-short circuit condition between any other pairof' wires,

only one lamp will be extinguished asin the other test. r

Another difference between the two tests lies in the fact that a shorted condition between con ductors H, l2, l3, and Id and-a similar condition between all five conductors cannot be distinguished, as either condition will-extinguish all of the indicating lamps. Elowever, a short circuit between fourof the five wires, one of which is conductor 613, will indicate which wire isgnot shorted to these four. For example if conductors Ii, [2, l3, and 6d are shorted togetheryindicating lamps 30, 58, and 29 in the arms 24; 54,-

. 4 relays requires the maintenance of the. proper phase relationship between the two source voltages.

. In addition to its use in the testing of a plurality of conductors, the invention is well suited to the testing .of telephone jack circuits, as it provides a simultaneous test for short circuits between the} tip, ring, sleeve, and frame elements, with immediate indication and designation of any defect.

It is to be understood that the above described arrangements are simply illustrative of the application of the principles of the invention. Numerous other arrangements maybe readilydevised bythose skilledin the art whichywillembody the principles of the invention and fall with inthespiritand scope thereof. 7

What'is claimed is: K H r '1. Test apparatus comprising four terminals for receivin conductors to be tested, four indicating devices. connecting theterminals togetheras a bridge in conjugate pairs,- other indicating devices interconnecting the terminals'of each pair, meansfor applying an alternatingpotential between the two terminals'of one pairandmeans ceiving conductors to be tested, two other: indi eating devices each connectedibetween-a pair of alternate terminals of the loop and means for eating devices serially connected in a closed. loop with terminals between the devices for receiving conductors to be tested, connections between: the pairs of alternate terminals, said connections being joined and includin fourother indicating 'devices each connected between said juncture and a terminal, and means for. applying two alternating potentials essentially in quadrature with each otheracross the two alternate'pairs of terminals. I a f 4. Apparatus for indicating continuity of con ductors comprising four indicating devices serl-' iallyconnected. in a closed loop with terminals between the devices for receivin lthe. adjacent ends of conductors to be tested, two otherlin-i dicating devices each connected between .a .pair of alternate terminalsv of the loopgmeans for. applying two alternating potentials:essentially in quadrature with each other acrossithe two alternate pairs of terminals, and means for connecting the conductors together at the ends remote from the terminals. i. I p

" JESSE A.CRANFGRD,

REFERENCES CITED Thefollowing references are of recordinthe file of :thispatent:

UNITEns ATEs PATENTS Number Name Date' 761,280 Woodblidge Q May 31, .1904

2,447,625. .AStlIl Al.1g.- 24, .1948

2,567,859; Ringo Sept. ll, 11951 

